The present invention relates to the field of semiconductors, and, more particularly, to a method and associated apparatus for removing encapsulant from a device, such as to facilitate failure testing of the device.
Semiconductor devices in the form of integrated circuits are used in virtually all electronic devices. A typical integrated circuit includes a die formed of silicon with transistors and other active and passive devices formed on the silicon. The integrated circuit die is typically included in an integrated circuit package. The package typically provides for the die: electrical interconnection, mechanical support, heat dissipation, and protection.
Most integrated circuit packages include a leadframe which carries the external connection pins, wire bonds between the leadframe and the die, and an encapsulant. The encapsulant is typically a plastic which is molded around the other components and cured during manufacturing to thereby protect the encapsulated components from the ambient environment. Ceramics are used in some applications as the encapsulating material, but are more expensive and require higher energy processing as compared to plastics.
Thermosetting epoxy materials are typically used for plastic packages. These materials are typically made with fused silica as a filler, such as greater than 60% by weight. The epoxy may include cresylic novolac resin and phenolic novolac resin as the hardener. In addition, a flame retardant, such as antimony trioxide or bromine is included. The thermosetting epoxy is permanently cured, typically by the application of heat, during the molding process.
It is often desirable to non-destructively access the integrated circuit die after the packaging has been completed. For example, if device testing indicates that the integrated circuit is defective, it is often desirable to perform an analysis to determine what caused the failure. The results of the failure analysis may be useful to change one or more manufacturing techniques to thereby reduce the number of future defects.
Unfortunately, removal of the encapsulant material from the integrated circuit is not a simple process. The thermosetting encapsulants typically used will not simply reflow upon the application of heat thereby exposing the underlying leadframe, bond wires and circuit die. It is typically important for subsequent testing that the die and bonding system not be destroyed, and that electrical connections can be established to facilitate electrical performance testing.
One conventional approach to removing the encapsulant or xe2x80x9cdecapsulatingxe2x80x9d an integrated circuit etches the encapsulant by applying concentrated acids, such as fuming nitric and fuming sulphuric acid or certain organic solvents, to the encapsulant. There are, of course difficulties with controlling the desired amount of etching, preventing damage to the interior metal components, and removing debris during the etching. Some of these difficulties are addressed, for example, in U.S. Pat. No. 5,766,496 to Martin which discloses an apparatus and associated method using an acid etch and wherein a first syringe pump pumps etchant into an etch head, and a second syringe pump agitates the first quantity of etching repeatedly into and out of an etched cavity. The etch head also includes a heater to heat the volume of etchant prior to its introduction against the encapsulant. Unfortunately, the apparatus and method still rely on the precise delivery and control of acid etchants.
U.S. Pat. No. 4,344,809 to Wensink discloses a jet etch apparatus for decapsulating the molded resin material from an integrated circuit device. The apparatus includes a jet pump or aspirator connected by a tube to an etching block. The etching block is further connected by a tube to a container for holding an etchant solution. The integrated circuit is placed on top of the etching block and as fluid flows through the jet pump, a suction is created drawing etching solution through the etching block and a hole is etched in the encapsulating material. The etchant solution is fuming sulphuric acid. U.S. Pat. No. 4,359,360 also discloses an approach using a heated etchant solution to jet etch the encapsulating material from an integrated circuit. Along these lines, U.S. Pat. No. 4,826,556 further includes a shield for shielding the integrated circuit from outside air to maintain pressure of the etchant fed by an etchant feed pump.
The hot acid etching decapsulating techniques may take from several minutes up to hours to remove the encapsulant. The acid etchant materials raise handling and disposal concerns. Controllability of the etching is also difficult and may result in destruction of the upper surface portions of the die and/or the bond pads. In addition, any ionic contamination at the surface of the die, as may be the cause of certain failures, would be typically be removed during acid etching.
Yet another conventional decapsulating technique includes exposing the integrated circuit to an oxygen plasma. Unfortunately, this approach may take several hours or even several days. In addition, the oxygen plasma etching equipment is relatively expensive.
In view of the foregoing background, it is therefore an object of the present invention to provide a method and apparatus for decapsulating an integrated circuit, such as to facilitate testing, for example, which is quick and which preserves the integrity of the underlying components.
This and other objects, features and advantages in accordance with the present invention are provided by a method for decapsulating an integrated circuit package by subjecting the encapsulant to electromagnetic radiation, and, more preferably microwave radiation, to break the polymer bonds of the polymer resin and convert the encapsulant to loosened particles. The loosened particles can then be removed to thereby decapsulate the integrated circuit package. The method may further include the step of maintaining the integrated circuit package below a predetermined temperature during the subjecting step. The step of maintaining the temperature below the predetermined temperature may be performed by controlling a power of the electromagnetic radiation, such as based upon sensing a temperature of the integrated circuit package. Since an integrated circuit package will typically include an integrated circuit die having one or more metal layers, the predetermined temperature is preferably below a melting temperature of the metal. It may also be desired to maintain a lower predetermined temperature less than about 350xc2x0 C.
To ensure uniform irradiation of the encapsulant, the method may further comprise the step of varying a frequency of the microwave radiation during the subjecting step. For example, the step of varying the frequency may comprise varying the frequency over a range of about 5 GHz to 8 GHz. Varying the frequency may also avoid damage from electrostatic fields.
The method may also include the step of positioning the integrated circuit within a shielded chamber during the subjecting step. In addition, the step of subjecting may comprise selectively subjecting a portion of the encapsulant overlying the integrated circuit die to the electromagnetic radiation.
The step of removing may comprise contacting and dislodging the loosened particles. For example, a brush may be used to remove the loosened particles. Alternately, the step of removing may comprise subjecting the loosened particles to a fluid stream, such as a nitrogen gas stream, for example. The loosened particles may also be removed under the influence of gravity.
The step of subjecting the integrated circuit package to microwave radiation is preferably carried out for a predetermined period of time in one variation of the invention. The step of subjecting may also be carried out until a predetermined portion of the encapsulating material has been converted to the loosened particles, as may be determined by observing the encapsulant.
Of course, the decapsulating method may be part of on overall process for studying an integrated circuit die after it has been incorporated into an integrated circuit package. According to this aspect of the invention, the method preferably further includes examining the exposed integrated circuit die after decapsulating the die.
The step of examining may comprise microscopically inspecting the exposed die. The step of examining may also include conducting at least one electrical test on the integrated circuit die, such as using the bond pads on the die which are left intact in accordance with a significant advantage of the present invention. The step of examining may also comprise conducting at least one chemical analysis test for contamination at an outer surface of the integrated circuit die. Again the ionic contamination, if present, remains at the die/encapsulant interface in accordance with another significant advantage of the present invention. Destructive physical analysis, such as including delayering of the die, may also be performed during the examination.
Another aspect of the present invention is directed to an apparatus for decapsulating an integrated circuit package. The apparatus preferably comprises a microwave shielded chamber, a support for supporting the integrated circuit package within the chamber, and a microwave generator coupled to the chamber for generating microwave radiation therein so as to subject the encapsulant of the integrated circuit package to microwave radiation to break polymer bonds in the polymer resin and convert the encapsulant to loosened particles. Moreover, the microwave generator preferably also includes frequency varying means for varying a frequency of the microwave radiation over a predetermined frequency range.
The apparatus may further include temperature control means for maintaining the integrated circuit package below a predetermined temperature while subjected to the microwave radiation. In one embodiment, the temperature control means comprises a temperature sensor and power control means for controlling a power of microwave generator responsive to the temperature sensor. In addition, the apparatus may also include means for removing loosened particles from the integrated circuit package.